Wireless health sensors that attach to the skin

Using metallic ink, researchers printed an antenna and sensor screen on an expandable sticker designed to adhere to the skin and monitor the heart rate and other health indicators and send these readings to the receiver on man. Image Credit: Bao Lab

Stanford engineers have developed experimental stickers that collect physiological signals radiated from the skin and then wirelessly transmit these health indications to a clothesline receiver. It's all part of a system called BodyNet.

We tend to take the protective function of our skin for granted, ignoring its other roles in subtle signals such as a flickering heart or a wave of embarrassment.

Now, Stanford engineers have developed a way to detect physiological signals emitted from the skin by sensors that cling like tape machines and wireless beam readings to a receiver attached to clothing.

To demonstrate this wearable technology, researchers glued wrist and abdominal sensors to a test to monitor a person's heartbeat and breathing, revealing how their skin tenses and contractes with each heartbeat or breath. Likewise, a person's elbow and knees stickers track the movements of the arms and legs, measuring the minute tightening or relaxation of the skin each time the muscle is flexed.

Jenan Bao, professor of chemical engineering whose lab described the system in August. Article 1

5 in Nature Electronics considers that this wearable technology, which they call BodyNet, will first be used in medical conditions, such as monitoring patients with sleep disorders or heart conditions. Her lab is already trying to develop new stickers to feel sweat and other secrets to track variables like body temperature and stress. Its ultimate goal is to create a range of wireless sensors that stick to the skin and work with smart clothes to track a greater variety of health metrics than the smartphones or watches consumers use today.

a day will be possible to create a set of sensors for the whole body to collect physiological data without interfering with the normal behavior of a person, "said Bao, who is also a KK Lee professor at the School of Engineering.

Extensive, comfortable, functional

PhD students Simao Niu and Naoji Matsuhisa led a team of 14 people who spent three years designing sensors. Their goal was to develop technology that is comfortable to wear and has no batteries or hard chains to prevent the stickers from stretching and sticking to the skin.

Their eventual design met these parameters by modifying RFID, a technology used to control keyhole entry into locked rooms. When a person holds an ID card to an RFID receiver, an antenna in the ID card collects a little bit of RFID energy from the receiver and uses this to generate code, which then returns it to the receiver.

The rubber sticker attached to the wrist can bend and stretch as the human skin moves, radiating the pulse readings to a receiver attached to the man's clothing. Image Credit: Bao Lab

The BodyNet sticker is similar to an ID card: It has an antenna that collects some of the RFID input energy from a receiver on clothes to power its sensors. It then takes the readings from the skin and returns them to the nearest receiver.

But in order for the wireless sticker to work, the researchers had to create an antenna that would stretch and bend like skin. They did this by screen printing metallic ink on a rubber sticker. However, whenever the antenna is bent or stretched, these movements make its signal too weak and unstable to be useful.

To avoid this problem, Stanford researchers have developed a new type of RFID system that can transmit strong and accurate signals to a receiver, despite constant fluctuations. The battery powered receiver then uses Bluetooth to periodically upload stickers data to a smartphone, computer, or other permanent storage system.

The original version of the stickers relies on small motion sensors to account for respiration and heart rate. Researchers are now exploring how to integrate sweat, temperature and other sensors into their antenna systems.

To move their technology beyond clinical applications and into user-friendly devices, researchers need to overcome another challenge – keeping the sensor and receiver close to each other. In their experiments, the researchers trimmed a receiver on the garment over each sensor. Pairing sensors and receivers one-to-one would be good in medical monitoring, but to create a BodyNet that anyone could wear during training, the antennas would have to be woven into clothing to receive and transmit signals without meaning where one puts a sensor.